Electrolytic refining of antimony



July 19, 1955 J. F. NEELY ELECTROLYTIC REFINING OF ANTIMONY Filed May22, 1951 LAU/VDEI? United States Patent '0 This invention relates to inelectrolytic refining of new and useful improvements antimony. Moreparticularly, the invention relates to the use of a plating tank havinga plurality of spaced plates, one end plate being an anode and theopposite end plate being a cathode, each of said plates being aperturedto permit a gradual, re-

stricted flow of electrolyte from one end of the tank to the other, allof said plates being supported within the plating tank. With such anarrangement, each plate, other than the end plates, becomes cathodic onone surface and anodic on the opposite surface and metal will bedeposited on the cathode side of each plate, assuming that suflicientelectromotive force, current and concentration of electrolyte areemployed.

One feature of the invention is a means whereby the individual platesmay be mounted in the plating tank. For each plate an inflatable rubbertube is fixed along the sides and bottom of the tank, in the generalform of a U, the plate fitting against the tube. When the tube isinflated, the plate is forced against the side of the tube and the tubeis forced against the sides and bottom of the tank, thus preventingcirculation of liquid past the edges of the plate. The inflatable tube,therefore, provides a convenient means facilitating installation andwithdrawal of plates. It will be understood that other means forsupporting the plates in the tank may be employed.

The apparatus employed is singularly compact and inexpensive toconstruct and operate. Particularly, the plating tank occupies a verysmall space compared with other plating tanks of comparable capacity, isquite i11- expensive to construct, and the cost of operation is low.

One adaptation of the invention is in the electrolytic reduction ofantimony from stibnite, a process which has not heretofore beensuccessfully accomplished on a commercial scale. The instant processmakes possible the use of low-grade stibnite, which aboundsdomestically, whereas smelting processes in common use require ahigh-grade ore which is not domestically produced in suflicientquantities.

The process involves the dissolving of ground ore in a caustic solventsuch as sodium hydroxide, the filtering of the pregnant solution toremove undissolved ore and dross, the plating of the pregnant solutionto deposit out the metal in a tank such as has been described, therecovery and make-up of the solvent, and the scraping of the depositedmetal from the plates.

The apparatus and method are useful in plating of metals and in theelectrolytic reduction of various ores. In the reduction of oresdirectly to metal by electrolytic deposition, in addition to thechemical problems involved in determining the solutions best suited toextracting the metallic content from the ground ore, there is anelectrical problem involved which has not heretofore been solved byexisting and known methods. The deposition of metal from pregnantsolutions on the cathode plates of electrolytic cells is accomplished atlow voltages and the voltage must be accurately regulated. In the usualconstruction of an electrolytic cell, it is customary to employ a numberof metallic plates, spaced, and alternately anode and cathode, thereusually being one more anode plate than cathode. The anode plates, beingthe positive electrical connection required,

each to the other. The results in a great multiplicity of electricalconnections which must be so arranged that they may be quickly andeasily disconnected from the cathode plates in order that the cathodeplates may be removed wherever it is desired to scrape off the metalwhich has been deposited thereon from the pregnant solution.

In the very nature of an electrolytic action gases are released andexcessive corrosion takes place at all of this multiplicity ofelectrical connections. Using a direct current at very low voltages(usually of the order of two a very short wire or other metal connectionbesultant metallic deposit.

The electrolytic cell hereinafter described overcomes these obstacles inthat, in effect, i

be required.

By the hereinafter described means and method is assured limited by thespecific For convenience of description of the invention, it will beassumed that the process and apparatus are employed in the deposition ofantimony from its ore, it being understood that the invention is capableof other uses within the scope of the appended claim.

The solvent used to dissolve the ore is a caustic, preferably NaOH.

The ore may be stibnite, ground to 20 mesh or finer. One of the featuresof the invention, as has been stated, is that the ore may be low grade.Further, the invention may be used to work over ore dumps of smeltingand flotation plants wherein the dumps contain an appreciable quantityof antimony.

The ore is deposited in inner tank 11 having a filter 12 along itsbottom, larger tank 13. Solvent is continuously allowed to flow intoinner tank 11 from storage tank 14, thus contacting the ore anddissolving out the antimony. In order to improve the action, the innertank 12 may be vibrated by any convenient means. After all the charge ofore in inner tank 11 has been exhausted, the inner tank is removed anddumped and a fresh supply of ore deposited in inner tank 11. Thepregnant solution or electrolyte produced is preferably at about 2%saturation. Such a solution results, for example, from use of 100 poundsof 3% ore in 300 to 350 pounds of solvent. The resulting pH rangesbetween 5 and 8, preferably 7.

The solution resulting from the action, together with a certain amountof undissolved material and impurities, passes through filter 12 in thebottom of inner tank 11 and is discharged adjacent the top of outer tank13, thereupon flowing into the bottom of first launder tank 16. Saidfirst launder tank is divided into two substantially equal compartmentsby horizontally disposed ceramic filter 17, which separates out most ofthe impurities in the electrolyte, the impurities sinking to the bottomand being periodically removed. Adjacent first launder tank 16 is secondlaunder tank 18 receiving the purified electrolyte from the top of firstlaunder tank; additional impurities sink to the bottom of this tank. Itwill be understood that filter material may be employed in secondlaunder tank 18, if required.

From the top of second launder tank the purified pregnant solution mayflow into plating tank 19, or, optionally, into a pregnant solutionstorage tank (not shown) from which it may later be drawn off intoplating tank 19.

Plating tank 19 involves certain structural features. It is preferablygenerally rectangular in cross-section and fashioned of wood or othermaterial not readily affected by the solutions employed. Supportedwithin tank 19 is a plurality of transverse plates 21, such as ironplates inch thick, spaced apart 2 inches. An even number of plates 21 isemployed. Plates 21 are vertically mounted in tank 19, one convenientmeans being by use of an inflatable rubber tube 22, shown incrosssection in Fig. 4, each said tube 22 being permanently affixed tothe sides and bottom of tank 19. The inner edges of tube 22 are providedwith wings 23 extending out from the tube body and adapted to engage andsecure opposite surfaces of plate 21 along the edges thereof. Said tubes22 are U-shaped and molded to fit in the manner shown in said Fig. 4.The space between wings 23 forms a slot within which plates 21 mayslide. A valve 24 is fitted to each tube so that the tubes may beinflated and deflated, and upon inflation form a watertight seal betweenplates 21 and the sides and bottom of tank 19. By this or other means,plating tank 19 is separated into a plurality of compartments by plates21. When it is desired to remove a plate, tube 22 surrounding the edgesthereof is deflated, permitting plate 21 to be withdrawn.

It will be understood that other means may be employed to divide tank 19into a plurality of cells. For example, resilient tubes which are notinflatable may be employed. It is important, however, that the plates beheld in the tank in such manner that leakage of solution around theedges is minimized, yet the plates may readily be withdrawn.

The invention is useful in plating metals from solutions of variousmetals. Thus it is not necessary that said tank being suspended withinthe metal in the pregnant solution be derived directly from ore, as hasbeen described, for electrolytes derived from other sources may beemployed. From whatever source, pregnant solution flows into one end oftank 19 through port 26 from second launder tank 18 or any other source,and first plate 21a acts as a baflle preventing direct flowlongitudinally through the tank. However, the first and alternate platesare provided with a row of small holes 27 of, for example, A in.diameter, spaced upwardly a short distance from the bottom edge of saidplates. Intermediate plates are provided with similar small holes 27spaced downward from the upper edges. Thus a circuitous flow ofelectrolyte is provided down between one pair of plates and up betweenthe next, said flow being maintained out through discharge port 28 inthe end of tank 19 opposite port 26. Valve 29 is provided in thedischarge line, said valve being regulated to maintain the liquid levelsuch that tank 19 does not overflow.

First plate 21a is made an anode by connection in conventional mannerwith the positive side of a source of direct current. The last plate,there being preferably an even number of plates, is made a cathode. Thevoltage impressed is the number of plates multiplied by two volts-i. e.if twenty plates are used, the desirable voltage is 40 volts. If morethan six volts per plate are used, there is a tendency for holes to formin the plates, and if substantially less than two volts are used, thereis insufiicient electromotive force to accomplish plating. The currentdensity is between 7 and 9 amps per square foot of surface area perplate. It will be understood that optimum voltages and amperages varydependent upon the metal being plated. Since there is no directelectrical connection between the source of current and the intermediateplates, each plate sets up its own cell action, giving each plate apositive effect on one side and a negative effect on the other side andthis causes the metal to be deposited on the negative side of eachintermediate plate. When the coating has built up to an extent that itbridges the gap between plates or tends to scale off and fall to thebottom of the tank, the plates are removed by deflating tubes 22 (ifsuch means is employed to hold the plates) and pulling the plates out bylifting holes 31 along the top edges. Since there are no electricalconnections on intermediate plates, the multiplicity of connections anddisconnections employed in conventional plating apparatus is avoided.After removal, plates 21 are scraped to remove the metal deposited.

Solution flowing from plating tank 19 passes through 3-way valve 32 andthence to one or the other of foot tanks 33. Said foot tanks 33 arealternately filled from plating tank 19, and after each tank 33 isfilled sufficient caustic or other solvent used is added to build up therequired strength of solution, and the contents are then pumped by pump34 back up to storage tank 14 for recirculation.

It will be understood that whereas a preferred embodiment of theinvention has been described and illustrated, changes may be madetherein without departing from the spirit of the invention and the scopeof the appended claim.

What is claimed is:

A method of refining antimony for stibnite comprising, dissolving outthe metal in said stibnite with sodium hydroxide solvent; filtering outundissolved ore and dross; laundering the filtered pregnant solution;and depositing out said antimony by continuously flowing said pregnantsolution as an electrolyte in a continuous, circuitous path through aplurality of adjacent cells continuously communicating one with theother through restricted apertures, said cells being defined byremovable, parallel iron plates, and passing an electric current througheach of said cells, by making the end plate through which said solutionenters an anode and the opposite end plate House Feb. 5, 1895 ElmoreAug. 21, 1897 6 2,212,588 Csanyi Aug. 27, 1940 2,331,395 Holmes Oct. 12,1943 2,542,989 Carter et a1 Feb. 27, 1951 OTHER REFERENCES Report ofInvestigations No. 3491, Feb. 1940, Bureau of Mines, by J. Koster and M.B. Royer pages 4 and 5.

